High toughness spheroidal graphite cast iron and method for producing the same

ABSTRACT

According to this invention, 0.0035 - 0.02 % of N is contained in a spheroidal graphite cast iron to result in ferrite and pearlite structures. This spheroidal graphite cast iron is markedly improved in toughness. This invention further provides a method for producing a high toughness spheroidal graphite cast iron which comprises adding N to a melt of a cast iron during or after spheroidizing treatment to contain 0.0035 - 0.02 % of N in compositions of said cast iron.

United States Patent 1191 Nakae et a1.

1 1 June 24, 1975 1 HIGH TOUGHNESS SPHEROIDAL GRAPHITE CAST IRON AND METHOD FOR PRODUCING THE SAME [75] Inventors: Hideo Nakae, Kashiwa; Akihiro Goto, Tokyo, both of Japan [73] Assignee: Hitachi, Ltd., Japan [22] Filed: Jan. 4, 1974 [21] Appl. No.: 430.681

[30] Foreign Application Priority Data Jan. 24. 1973 Japan 48-9530 [52] US. Cl. 75/130 R; 75/53; 75/123 CB [51] Int. Cl. C220 37/04 [58] Field of Search 75/123 CB. 130 R. 59. 53

[56] References Cited UNITED STATES PATENTS 3.013.911 12/1961 Peras 75/130 R 3.133.813 5/1964 Ruff 75/130 R 3.177.072 4/1965 Kaess 75/130 R 3,257,197 6/1966 Death 75/59 3,309,197 3/1967 Kusaka... 75/130 R 3.321.304 5/1967 Snow 75/53 3.492.118 1/1970 Mickelson 75/130 R 3,767,386 10/1973 Ueda 75/123 CB Primary E.\'aminerP. D. Rosenberg Attorney, Agenl, 0r Firm-Craig & Antonelli 1 57] ABSTRACT 13 Claims, No Drawings HIGH TOUGHNESS SPHEROIDAL GRAPHITE CAST IRON AND METHOD FOR PRODUCING THE SAME BACKGROUND OF THE INVENTION This invention relates to a high toughness spheroidal cast iron and a method for producing the same.

In case of the general spheroidal graphite cast iron, elongation is decreased with increase in tensile strength or tensile strength is decreased with increase in elongation. Therefore, conventionally, when high strength and high ductility are required, the cast iron has been subjected to quenching and tempering treatment or some alloying elements capable of increasing strength and ductility have been added thereto. However, although the former method may be applicable to a casting of simple shape such as test piece, it cannot be applied to that of complicated shape such as actual casting. On the other hand, according to the latter method, expensive alloying elements must be used and so the production cost is in creased and furthermore control of return becomes complicated.

There have been various reports as to addition of N to spheroidal graphite cast iron. The representative thereof which was reported at I. F. C. (International Foundry Congress) is as follows: Even when potassium ferrocyanide [K Fe(CN) is added to a melt mainly composed of C 3.473.64%, Si 1.96-2.34% and Mn 0.1380.162% before spheroidizing treatment, most of N in the melt escapes due to spheroidization and it tends to be converted into white iron. Furthermore, it was reported that thus obtained spheroidal graphite cast iron has much cementite in structure.

Therefore, it is supposed from the amount of cementite formed therein that said spheroidal graphite cast iron has a tensile strength of about 60 kgfmm an elongation of l-2% and a hardness (HB) of about 300.

From said report, it cannot be anticipated that addition of N results in increase in toughness, although it can be recognized that hardness is increased.

OBJECT OF THE INVENTION The object of this invention is to provide a spheroidal graphite cast iron markedly improved in elongation without lowering its tensile strength and a method for producing the same.

SUMMARY OF THE INVENTION This invention provides a spheroidal graphite cast iron which comprises, by weight, 3.24.0% of C,

2.0-3.8% of Si, not more than 1.0% of Mn, not more than 0.1% of spheroidizing element, 0.00350.02%, preferably ODDS-0.013% of N and the balance Fe and incidental impurities and the structure of which is spheroidal graphite, ferrite and pearlite.

Furthermore, this invention provides a method for producing a spheroidal graphite cast iron which comprises adding N to a melt of cast iron during or after spheroidizing treatment to obtain a spheroidal graphite cast iron having the compositions of 32-40% of C, 2.0-3.8% of Si. not more than 1.0% of Mn, not more than 0.1% of spheroidizing element, 0.0035-0.02% of N and the balance Fe and incidental impurities and having spheroidal graphite, ferrite and pearlite structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS This invention will be explained with reference to Examples to show that a spheroidal graphite cast iron having markedly improved elongation can be obtained without lowering its tensile strength.

Various spheroidal graphite cast irons having the compositions as shown in Table 1 were molten and the melts were cast in Y block having 1 inch width. Test piece was taken from each casting thus obtained and the test piece in as-cast state was subjected to tensil test and hardness test. The results obtained were shown in Table 2.

In table 1, sample No. 1-3 are the conventional spheroidal graphite cast irons and No. 4-19 are the spheroidal graphite cast iron of this invention.

Table l No. C Si Mn Mg N Fe 1 3.78 2.80 0.15 0.05 0.0023 Balance 2 3.80 2.68 0.37 0.05 0.0027 3 3.66 3.23 0.74 0.04 0.0025 4 3.70 3.04 0.47 0.0040 5 3.68 2.98 0.47 0.0060 6 3.69 2.95 0.56 0.009 7 3.60 3.70 0.48 0.05 0.0185 8 3.57 2.48 0.29 0.0076 9 3.60 2.56 0.31 0.0080 10 3.62 2.67 0.09 0.0087 11 3.66 3.23 0.74 0.0048 12 3.62 3.10 0.74 0.04 0.0074 13 3.70 3.12 0.61 0.0134 14 3.68 2.48 0.51 0.0051 15 3.58 2.51 0.55 0.0060 16 3.62 2.51 0.58 0.0072 17 3.65 2.50 0.60 0.0090 18 3.70 2.80 0.75 0.0095 19 3.72 2.83 0.80 0.0115

Table 2 Tensile Elong Hard- No. N additive Method for Strength ation ness addition of N kg/mm H8 1 None 49.0 18.0 2 62.0 11.0 212 3 72.4 2.0 262 4 Fe-Cr-N During 5 8.1 18.6 188 Spheroidization 5 54.5 19.8 183 6 Fe-Mn-N 56.5 18.8 183 7 Hexamine After 5 8.4 20.6 193 Spheroidimtion 8 Fe-Mn-N 46.7 21.2 153 9 During 45.1 24.8 154 Spheroidization 10 Fe-Cr-N After 48.9 21.6 160 Spheroidization 11 Fe-Mn-N 69.3 6.6 235 12 71.7 6.4 241 13 Fe-Cr-N 72.7 7.0 241 14 Fe-Mn-N During 64.0 14.2 198 Spheroidization 15 63.5 15.0 198 16 64.7 15.2 195 17 60.2 16.0 195 1.8 After 75.2 5.0 270 Spheroidization 19 76.2 4.5 275 It is recognized from Table 2 that the conventional spheroidal graphite cast irons No. l-3 had a tensile strength of 49.0 kg/mm, 62.0 kg/mm and 72.4 kg/mm while they had low elongation of 18%, 11% and 2% in connection with their tensile strength and the spheroidal graphite cast irons No. 4-19 of this invention had markedly increased elongation in connection with their tensile strength.

It was observed that the matrix structure of the cast iron was ferrite and pearlite and especially the amount of ferrite structure was increased by a large amount by addition of N.

Furthermore, it was confirmed from these experiments that the cast iron which shows the best characteristics in this invention is one which contains 0.005-0.013% of N in addition to the basic components of C, Si, Mn and Mg.

The reasons for limitation of the ranges of the elements as mentioned before in the spheroidal graphite cast iron of this invention are as follows:

C is essential for production of spheroidal graphite cast iron. When content ofC is less than 3.2%, it tends to become white iron and is not suitable for use and when more than 40%, graphite dross is produced due to floatation of graphite during solidification of cast iron. Thus, the rang ofC content is limited to 32-40%.

When content of Si is less than 2.0%, the cast iron is apt to become white iron and when more than 3.8%, transition temperature is higher than room temperature and the cast iron becomes brittle. Therefore, the range of Si content is limited to -38%.

When content of Mn is more than 1.0%, the cast iron becomes white pig iron and hence it is limited to not more than 1.0%.

When spheroidizing elements such as Mg and Ca are contained in an amount of more than 0.1%, the cast iron is apt to become white pig iron and also dross may form. Therefore, content thereof is limited to not more than 0.1%. As the spheroidizing elements, any of the known spheroidizing agents, for example, Mg, Ca, Ce, MgCa, MgCe, MgCa-Ce, etc. may be used.

When content of N is less than 0.0035%, elongation is not improved so much and when more than 0.02%, casting defects are brought about and the cast iron is apt to become white pig iron. Therefore, content on N is limited to 0.00350.02%.

What is claimed is:

l. A high toughness spheroidal graphite cast iron which comprises, by weight, 32-40% of C, 20-38% of Si, not more than 1.0% of Mn, not more than 0.1% ofa spheroidizing element, 0.00350.02% of N and the balance Fe and incidental impurities, said cast iron having a matrix structure which comprises ferrite and pearlite.

2. A spheroidal graphite cast iron according to claim 1, wherein it contains 0005-0013% of N.

3. A method for producing a high toughness spheroidal graphite cast iron, which comprises adding N to a melt of cast iron containing C, Si and Mn as basic components during spheroidizing treatment to result in a composition containing 32-40% of C, 20-38% of Si, not more than 1.0% of Mn, not more than 0.1% of a spheroidizing element, 0.00350.02% of N and the balance Fe and incidental impurities and thereafter forming ferrite and pearlite structures from said composition.

4. A spheroidal graphite cast iron according to claim 1, wherein said spheroidizing element is selected from the group consisting of Mg, Ca, Ce, MgCa, MgCe and MgCa-Ce.

5. A spheroidal graphite cast iron according to claim 4, wherein said cast iron consists essentially of, by weight, 32-40% of C, 20-38% of Si, not more than 1.0% of Mn, not more than 0.1% ofa spheroidizing element, 0.00350.02% of N and the balance Fe and incidental impurities.

6. A spheroidal graphite cast iron according to claim 5, wherein said cast iron consists of, by weight, 32-40% of C, 20-38% of Si, not more than 1.0% of Mn, not more than 0.1% of a spheroidizing element, 0.00350.02% of N and the balance Fe and incidental impurities.

7. A method according to claim 3, wherein said spheroidizing element is selected from the group consisting of Mg, Ca, Ce, MgCa, MgCe and Mg- CaCe.

8. The process of claim 7, wherein said composition consists essentially of, by weight, 32-40% of C, 20-38% of Si, not more than 1.0% of Mn, not more than 0.1% ofa spheroidizing element, 0.00350.02% of N and the balance Fe and incidental impurities.

9. The process according to claim 8, wherein said composition consists of, by weight, 32-40% of C, 20-38% of Si, not more than 1.0% of Mn, not more than 0.1% ofa spheroidizing element, 00035-0.02% of N and the balance Fe and incidental impurities.

10. A method for producing a high toughness spheroidal graphite cast iron, which comprises adding N to a melt of cast iron containing C, Si and Mn as basic components after spheroidizing treatment to result in a composition containing 32-40% of C, 20-38% of Si, not more than 1.0% of Mn, not more than 0.1% of a spheroidizing element, 0.00350.02% of N and the balance Fe and incidental impurities and thereafter forming ferrite and pearlite structures from said composition.

11. The process according to claim 10, wherein said spheroidizing element is selected from the group consisting of Mg, Ca, Ce, MgCa, MgCe and Mg- CaCe.

12. The process according to claim 11, wherein said composition consists essentially of, by weight, 32-40% of C, 20-38% of Si, not more than 1.0% of Mn, not more than 0.1% of a spheroidizing element, 0.00350.02% of N and the balance Fe and incidental impurities.

13. The process according to claim 12, wherein said composition consists of, by weight, 32-40% of C, 20-38% of Si, not more than 1.0% of Mn, not more than 0.1% ofa spheroidizing element, 0.00350.02% of N and the balance Fe and incidental impurities. 

1. A HIGH TOUGHNESS SPHEROIDAL GRAPHITE CAST IRON WHICH COMPRISES, BY WEIGHT, 3.2-4.0% OF C, 2.0% OF A SPHEROIDIZING THAN 1.0% OF MN, NOT MORE THAN 0.1% OF A SPHEROIDIZING ELEMENT, 0.0035-0.025% OF N AND THE BALANCE FE AND INCIDENTAL IMPURITIES, SAID CAST IRON HAVING A MATRIX STRUCTURE WHICH COMPRISES FERRITE AND PEARLITE.
 2. A spheroidal graphite cast iron according to claim 1, wherein it contains 0.005-0.013% of N.
 3. A method for producing a high toughness spheroidal graphite cast iron, which comprises adding N to a melt of cast iron containing C, Si and Mn as basic components during spheroidizing treatment to result in a composition containing 3.2-4.0% of C, 2.0-3.8% of Si, not more than 1.0% of Mn, not more than 0.1% of a spheroidizing element, 0.0035-0.02% of N and the balance Fe and incidental impurities and thereafter forming ferrite and pearlite structures from said composition.
 4. A spheroidal graphite cast iron according to claim 1, wherein said spheroidizing element is selected from the group consisting of Mg, Ca, Ce, Mg-Ca, Mg-Ce and Mg-Ca-Ce.
 5. A spheroidal graphite cast iron according to claim 4, wherein said cast iron consists essentially of, by weight, 3.2-4.0% of C, 2.0-3.8% of Si, not more than 1.0% of Mn, not more than 0.1% of a spheroidizing element, 0.0035-0.02% of N and the balance Fe and incidental impurities.
 6. A spheroidal graphite cast iron according to claim 5, wherein said cast iron consists of, by weight, 3.2-4.0% of C, 2.0-3.8% of Si, not more than 1.0% of Mn, not more than 0.1% of a spheroidizing element, 0.0035-0.02% of N and the balance Fe and incidental impurities.
 7. A method according to claim 3, wherein said spheroidizing element is selected from the group consisting of Mg, Ca, Ce, Mg-Ca, Mg-Ce and Mg-Ca-Ce.
 8. The process of claim 7, wherein said composition consists essentially of, by weight, 3.2-4.0% of C, 2.0-3.8% of Si, not more than 1.0% of Mn, not more than 0.1% of a spheroidizing element, 0.0035-0.02% of N and the balance Fe and incidental impurities.
 9. The process according to claim 8, wherein said composition consists of, by weight, 3.2-4.0% of C, 2.0-3.8% of Si, not more than 1.0% of Mn, not more than 0.1% of a spheroidizing element, 0.0035-0.02% of N and the balance Fe and incidental impurities.
 10. A method for producing a high toughness spheroidal graphite cast iron, which comprises adding N to a melt of cast iron containing C, Si and Mn as basic components after spheroidizing treatment to result in a composition containing 3.2-4.0% of C, 2.0-3.8% of Si, not more than 1.0% of Mn, not more than 0.1% of a spheroidizing element, 0.0035-0.02% of N and the balance Fe and incidental impurities and thereafter forming ferrite and pearlite structures from said composition.
 11. The process according to claim 10, wherein said spheroidizing element is selected from the group consisting of Mg, Ca, Ce, Mg-Ca, Mg-Ce and Mg-Ca-Ce.
 12. The process according to claim 11, wherein said composition consists essentially of, by weight, 3.2-4.0% of C, 2.0-3.8% of Si, not more than 1.0% of Mn, not more than 0.1% of a spheroidizing element, 0.0035-0.02% of N and the balance Fe and incidental impurities.
 13. The process according to claim 12, wherein said composition consists of, by weight, 3.2-4.0% of C, 2.0-3.8% of Si, not more than 1.0% of Mn, not more than 0.1% of a spheroidizing element, 0.0035-0.02% of N and the balance Fe and incidental impurities. 